Field of the Invention
The invention relates to a control unit for a combustion engine for determining at least one reference variable for a combustion engine.
Control units are used to control important engine functions in the vehicle field. In particular, they are used, in addition to design-engineering measures such as combustion chamber design and the influence on mixture formation by injection systems and injection methods, to reduce fuel consumption and the related CO2 emissions and significant exhaust gas components such as carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) as well as carbon black and particles during engine operation.
Known functions of a control unit receive information about an operating state of the engine (for example revolution rate, torque, desired torque, temperature, DPF (Diesel Particle Filter) loading) and determine reference variables that influence consumption and emissions during operation.
For determining these reference variables, engine characteristic fields that are also stored in the control unit are often used, in which for example a setpoint exhaust recirculation rate or a setpoint charging pressure are stored depending on the aforementioned operating state.
Suitable reference variables are for example exhaust recirculation rate, exhaust recirculation distribution, filling, injection point in time and ignition point in time. Control variables (for example choke flap position, position of a VTG (Variable Turbine Geometry)) are then derived from the reference variables.
The term “combustion engine” includes in this context the entire combustion engine system with all the units, auxiliary units and control elements thereof.
With this strategy, it can be ensured that the upper emission limits are not exceeded in specified speed profiles by an optimized assignment of certain reference variables. Standard driving cycles are an example of such speed profiles, for example the NEDC (New European Driving Cycle), which are driven to determine the exhaust and/or consumption values. For such cycles, for example global optimization approaches are known, as specified in Heiko Sequenz: Emission Modelling and Model-Based Optimisation of the Engine Control, D17 Darmstadt Dissertations 2012.
During real driving operations (and possibly during the so-called Real Driving Emissions Test Method) different arbitrary speed profiles and operating states occur, which are unknown before and during the trip.
As the individual operating states already include different emission values independently of the engine control, the consumption and emission values (I/100 km or mg/km) can sometimes deviate significantly downwards or upwards in these different arbitrary driving profiles. The global optimization of for example fuel consumption or CO2 emissions while not exceeding emission limits is thus no longer provided by the known control strategies.
In particular, with competing emission variables, such as occur for example in a diesel engine during carbon black (particle) emissions and oxides of nitrogen emissions, situations can occur in which for example the permissible oxides of nitrogen emissions are exceeded and the carbon black emissions fall significantly below permissible carbon black emissions in a speed profile.